Install bluetooth audio VINTF fragment in apex

Previously, android.hardware.bluetooth.audio-impl was installed with no
use and the attached vintf was fulfilled by the
com.android.hardware.audio apex.

For cleanup, we no longer install android.hardware.bluetooth.audio-impl
separately (for cuttlefish) and install the VINTF inside the apex.

Bug: 312265159
Test: atest VtsHalBluetoothAudioTargetTest
Change-Id: I31e0ccd6a8c3c00565159f2be7fe3bf4d70e9ddf

audio/aidl/default/apex/com.android.hardware.audio/Android.bp

@@ -45,6 +45,7 @@ apex {
     prebuilts: [
         "android.hardware.audio.service-aidl.example.rc",
         "android.hardware.audio.service-aidl.xml",
+        "android.hardware.bluetooth.audio.xml",
         "audio_effects_config.xml",
     ],
 }

bluetooth/audio/aidl/default/Android.bp

@@ -40,3 +40,10 @@ cc_library_shared {
         "libbluetooth_audio_session_aidl",
     ],
 }
+
+prebuilt_etc {
+    name: "android.hardware.bluetooth.audio.xml",
+    src: "bluetooth_audio.xml",
+    sub_dir: "vintf",
+    installable: false,
+}